The present invention relates to a cord lock for a venetian blind lift cord.
Different forms of such cord lock are known in the art. One example known to the Applicants has a cord lock housing in which is rotatably mounted a pulley made from a plastic material, and a knurled rivet which can move up and down in slots in the housing. The lift cord for lifting and lowering the slots of the blind passes between the pulley and the rivet. When the lift cord is to be locked in position the rivet engaged by the cord travels upwardly, caused by the weight of the blind, and the cord becomes wedged between the rivet and the pulley. When the cord is pulled downwardly, the rivet drops and the blind is released. Experience has shown that such cord locks have a serious defect because of the plastic pulley. The cord used in venetian blinds is abrasive and wears grooves into the plastic pulley. As a consequence, the pulley does not rotate and the cord wears deeper and deeper grooves so that the cord eventually is no longer in the proper position relative to the rivet or cam locking the lift cord together with the pulley. As a result the lift cord cannot be locked. There may be other reasons for the failure of the pulley, such as that there is a slight flash of plastic molded onto the pulley and this flash fills the normal clearance and jams the pulley so that it cannot rotate. Any foreign matter, such as sawdust or plastic or metal chips, becomes wedged in the clearance between the pulley and the housing of the cord lock, and prevents the rotation of the pulley.
Furthermore, the pulley may freeze at the walls of the cord lock housing. Failure results quickly because the frozen pulley will be heated by the friction generated by the lift cord rubbing against the pulley and this will warm and soften or melt the plastic of the pulley.
Replacing the plastic pulley by a metal one also has serious disadvantages. The pulley will squeal and because the cord lock is mounted in metal head rail the squeal will be amplified.
Using a miniature precision ball bearing to insure rotation of the pulley would be prohibitive because of cost.
It is an object of the present invention to overcome the various problems mentioned above caused by non-rotation of the pulley in the cord lock.
It is another object of the present invention to provide a cord lock that is simple in construction, and that can be manufactured easily and at low cost.